Work over the past year has been primarily refined earlier observations on gonococcal surface charge properties that accompany expression of Opa outer membrane proteins. Extensively studied were gonococci that express recombinant Opa proteins (rOpa?s) whose two major surface-exposed domains are identical to those found in wild-type OpaA, OpaB, and OpaC, are mosaics of these three Opa polypeptides, or have been deleted. The findings demonstrated that gonococcal surface charge is dramatically altered when different Opa proteins are expressed. Newly- employed techniques enabled correlation between observed bacterial cell surface charge and predictions of charge contributions of Opa proteins based on their known primary sequences. Gonococci typically acquire enhanced positivity (diminished negative charge) when they express an Opa protein, and the eleven different Opa?s comprising a single strain?s repertoire can confer a broad range of surface charges. But gonococci producing certain Opa proteins rapidly acquire highly negative charge when exposed to polyanions such as sulfated polysaccharides that "contaminate" in agar, DNA, and others. Thus, although OpaA contributes positive charge to gonococci, OpaA+ organisms can attain varying degrees of negativity depending on the type and amount of polyanions in the external milieu. Opa proteins that confer most positive charge endow the organisms with an ability to bind heparin, dextran sulfate, and the sulfated glycosaminoglycans on eukaryotic cells. The susceptibilities of rOpa+ gonococci to heparin correlates relatively well with bacterial cell surface charge and appears to relate inversely to an organism?s ability to bind heparin. It was also clear, from examination of organisms whose rOpa had a deletion of either of its two major exposed domains, that the overall affects of Opa expression are "cooperative" and not simply the sum of the properties individually conferred by these two domains.